C++ :

#include <cstdio>
#include <cstring>
typedef long long ll;
static const char* D = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
static int dig(char c){
    if(c >= '0' && c <= '9') return c - '0';
    if(c >= 'A' && c <= 'Z') return c - 'A' + 10;
    if(c >= 'a' && c <= 'z') return c - 'a' + 10;
    return 0;
}
int main(){
    char s[128], mp[64];
    if(scanf("%127s %63s", s, mp) != 2) return 0;
    /* 解析 "M->N" */
    int i = 0; ll M = 0, N = 0;
    while(mp[i] >= '0' && mp[i] <= '9'){ M = M * 10 + (mp[i] - '0'); i++; }
    while(mp[i] == '-' || mp[i] == '>' || mp[i] == '=') i++;
    while(mp[i] >= '0' && mp[i] <= '9'){ N = N * 10 + (mp[i] - '0'); i++; }
    if(M < 2 || N < 2){ printf("0\n"); return 0; }
    /* M 进制 -> 十进制 */
    ll v = 0;
    for(int k = 0; s[k]; k++) v = v * M + dig(s[k]);
    /* 十进制 -> N 进制 */
    if(v == 0){ printf("0\n"); return 0; }
    char b[80]; int k = 0;
    while(v > 0){ b[k++] = D[v % N]; v /= N; }
    for(int j = k - 1; j >= 0; j--) putchar(b[j]);
    putchar('\n');
    return 0;
}