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[References: 21 tit.]

The branching fractions of the doubly Cabibbo-suppressed decays D+ → K−K+K+, D+ → π−π+K+ and D+s → π−K+K+ are measured using the decays D+ → K−π+π+ and D+s → K−K+π+ as normalisation channels. The measurements are performed using proton-proton collision data collected with the LHCb detector at a centre-of-mass energy of 8 TeV, corresponding to an integrated luminosity of 2.0 fb−1. The results areB(D+→K−K+K+)B(D+→K−π+π+)=(6.541±0.025±0.042)×10−4,B(D+→ π−π+K+)B(D+→K−π+π+)=(5.231±0.009±0.023)×10−3,B(D+s→ π−K+K+)B(D+s→K−K+π+),=(2.372±0.024±0.025)×10−3,B(D+→K−K+K+)B(D+→K−π+π+)=(6.541±0.025±0.042)×10−4,B(D+→ π−π+K+)B(D+→K−π+π+)=(5.231±0.009±0.023)×10−3,B(Ds+→ π−K+K+)B(Ds+→K−K+π+),=(2.372±0.024±0.025)×10−3,where the uncertainties are statistical and systematic, respectively. These are the most precise measurements up to date.